The invention relates to providing improved interconnection between a leadframe and mold compound in a packaged semiconductor device; and, in particular, to providing an improved mechanical interference interlock to improve delamination performance in a quad flat non-leaded package (QFN) mold or other packaged semiconductor device.
FIGS. 1 and 2 are partial section views of a conventional packaged semiconductor device with a die pad 10 and a leadframe pad 11 adjacent to and spaced apart from the die pad 10. The drawings are shown on an enlarged scale, the size of the packaged semiconductor device being typically on the order of a few tens of millimeters. The leadframe pad 11 and the die pad 10 are encapsulated in a mold compound 12. A die (semiconductor chip) 13 is provided on the die pad 10 and is attached to the leadframe pad 11 by a bond wire 14. The leadframe has opposing side walls 15 and 16, a top surface 18 and a bottom surface 19 opposing the top surface 18. The top surface 18 and the bottom surface 19 are generally perpendicular to the opposing side walls 15 and 16. The bottom surface 19 of the leadframe pad 11 can be soldered to a board and is provided with a recess 17, which can also extend back from one of the side walls 16 that is nearest to the die pad. The recess 17 is formed by etching the leadframe pad 11 and is then filled with mold compound when the whole semiconductor package is encapsulated by the mold. The leadframe pad 11 is formed of a number of “fingers,” as seen in FIG. 2 which shows a side view of the packaged semiconductor device, looking at the side wall 15 furthest away from the die pad 10 on the outer edge of the device.
Many semiconductor devices may be manufactured in the same molded package and are then separated by a cutting step, which takes place after the die pad 10 and leadframe pad 11 have been encapsulated in the mold compound. In each package, the leadframe pads 11 of several adjacent devices may be formed as one common leadframe such that the devices are joined during formation. The common leadframe has an axis of symmetry between and parallel to the side walls 16, which will later form the side walls 15 of separate devices when cut.
FIG. 3 is a sectional side view illustrating the cutting step to separate two adjacent devices in the same package so as to arrive at the device shown in FIGS. 1 and 2. A saw blade 40 cuts along the axis of symmetry of the leadframe pad 11, perpendicular to an axis 41 which is parallel to the upper surface 18 of the leadframe pad 11. Two separate chips or dies are thus created.
Leadframes in packaged semiconductor devices that are pre-plated using NiPdAu or other finishes, however, have low adhesion to the mold compound in which the leadframe is encapsulated. This means that when individual chips or dies are separated by cutting, or are subject to temperature excursions, the leadframes can come loose from the encapsulating mold. This leads to separation from the bond wires, which risks that the device will not work and will be wasted. The invention has been devised with the foregoing in mind.